AO3-6585 Refactor work_info partials for emails to use tag_groups

[sarken]

Issue

https://otwarchive.atlassian.net/browse/AO3-6585

Purpose

Make the work_info partials more performant before we start using them for subscription emails. To quote this comment on an old subscription i18n PR:

The thing that stood out to me when I read the code is that the various *_string methods [currently used by the subscription email] use the tags association, so you only need a single database query for all of them (more or less). Whereas the work_info partial uses the individual ratings, categories, etc. associations, each of which is a separate ActiveRecord CollectionProxy that must be loaded with its own database query. I thought it was one database query per tag type, but it turns out it's three.

So this changes to tag_groups to reduce the number of database queries, as suggested in this comment on the issue.

Testing Instructions

Refer to Jira, but basically, we need to make sure gift notifications still work and look normal.

References

In the text above!

Credit

Sarken, she/her